The present invention is concerned with the measurement of the combined resistance to displacement of strings affixed in rackets used for playing games such as tennis, squash, racketball, and the like. Resistance to displacement is an important parameter since it has a direct relationship to the capability of the racket to control the direction and speed of the ball when it is struck.
Conventionally, the longitudinal tension of an individual racket string is measured. For example, in U.S. Pat. No. 3,831,442, which issued to Millard M. Cummins, et al on Aug. 27, 1974, a string tension measuring device is disclosed which engages a string and provides an indication of that string's longitudinal tension. Similarly, machines used in stringing rackets typically include suitable measuring means for indicating the tension imparted to a particular string as it is placed on the racket frame.
While the measurement of longitudinal tension of a string is useful, it does not provide a completely meaningful indication of the ability of the string racket to perform its intended function since other factors contribute to the resistance to displacement of the plane of strings which serves as the playing surface of the racket. Such factors include the size and shape of the racket head, the longitudinal and torsional rigidity of the head, the type of string and stringing technique used, stringing machine error, grommet friction in the racket, string relaxation after use, etc.